Handpiece of this kind having a heating device for heating media are known in particular in the case of dental spraying handpieces. The media used, such as water and air, must be heated to as constant a temperature as possible. However, this is very difficult to achieve in view of the different operating conditions. Disclosed in DE-OS 22 52 330 is a heating device with a through-flow heater in which the heating element is formed by a heating spiral. Heating spirals have the disadvantage that they require high heating power, are subjected to onerous demands on materials by the medium flowing by and cannot heat the media sufficiently uniformly. Furthermore, heating spirals cannot be used for continuous operation.
A device of the kind mentioned in the introduction is known from DE-OS 23 22 191. In this device a thermistor with a positive temperature coefficient, i.e. a barretter a low voltage, filament-type voltage regulator) of PTC-element, is used. In a comparatively complicated circuit the resistor operates as heater in the positive voltage half-wave and as sensor in the negative voltage half-wave, of which the output signal, together with the following circuitry, determines the current flow in the positive voltage half-wave. The double function of the thermistor has the disadvantage that there is only one voltage half-wave available for the heating phase so that the media are heated relatively slowly. Furthermore, there is the disadvantage that the control electronics are not separated from the heating device, so that maintenance of the heating devices is made difficult and exchange thereof is complicated.
A dental spraying handpiece is known from DE-OS 37 34 864 in which the electric heating devices, formed by means of heating spirals, form a detachable structural unit arranged in the handpiece.